The invention relates to a method for the manufacture of helical rotor blanks for helical gear machines in which a straight shaft of circular cylindrical shape is moved along the axis of said shaft, is rotated around said shaft axis and is formed without cutting. The invention further relates to a device for the application of this method.* FNT *Helical gear pumps are known e.g. from U.S. Pat. Nos. 2,527,673 to Byran, 2,603,161 to Lloyd and 3,139,035 to O'Connor, these pumps being said to be of the Moineau type. Motors of a corresponding type are known, e.g. from U.S. Pat. No. 3,879,094 to Tschirky et al.
In German Pat. (DE-PS) No. 1,703,828, a method is described for the manufacture of hollow, helical rotor blanks for helical gear from a tubular shaft, in which this shaft is re-shaped by a compression tool using a hoisting technique, said shaft being axially advanced and rotated in the intervals between the compression hoists. The forward motion along the shaft axis and the rotation around said axis thus take place step by step whenever the compression tool does not act upon the shaft. The compression tool comprises a ring consisting of segments through which the shaft can be moved and which, when its segments are closed, has an inner threaded surface with a conical pre-forming section and a cylindrical calibrating section, arranged behind it, as seen in the direction of the motion of the shaft.
Satisfactory results can be obtained with this method as long as precisely calibrated tubes are used as the basic material, said tubes having a relatively small wall thickness as compared to the tube diameter. However, such tubes with the required diameters and material quantities are not always available at advantageous prices. The use of the method of the prior art is further limited by the fact that one individual compression tool may be used for one rotor blank only, the diameter, eccentricity and axial pitch of which are precisely pre-determined; any deviation from one or several of the cited dimensions requires a separate compression tool or, at least a separate compression segment ring. In this manner, the manufacture of uncommon rotor sizes is so expensive that for such rotor size requirements the practice of using cutting tools is still adhered to, which, however, is not inexpensive because, depending on the rotor eccentricity, relatively large volumes have to be cut.
Another method is known, for instance from the German Pat. No. 1,091,072 and French Pat. No. 1,118,390, of manufacturing helical corrugated pipes by rotating a thin-walled smooth cylindrical tube around its axis and through a forming device which contains one or several forming rollers. The rollers are each rotatable around an axis which is adjusted at a slight angle to the longitudinal axis of the tube, corresponding to the axial pitch of the desired corrugated pipe. The rollers operate in the area of the front edge of a cylindrical arbor introduced into the smooth cylindrical inside of the tube and impress flutes into the wall of the tube, their axial pitch usually being only a small fraction of the outer diameter of the unshaped tube. The axial direction of the tube is not altered in this forming process. These devices of the prior art are useful only for the forming of thin-walled pipes and the cross-section of the rollers must be precisely adapted to the desired corrugated pipe profile. Using these devices, rotors or rotor blanks for helical gear motors or pumps whose axial pitch usually is a multiple of the original diameter of the shaft, cannot be manufactured even out of thin-walled tubes, much less can thick-walled pipes or rods with a solid cross-section be re-formed into rotor blanks.